Ceng4480 a1
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Sensors (v.1c) 1
JANGAM RAKESH KUMAR
SNIGDHA ROYSANJAY KALKAREPRIYA ANAMIKANEHA
Sensors (v.1c) 2
CENG4480_A1Sensors
Sensing the real world
Sensors (v.1c) 3
Sensors
Motion (Orientation/inclination )sensorsForce/pressure/strainPositionTemperature and humidityRotary positionLight and magnetic field sensors
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Motion (Orientation/inclination sensors
Acceleration GyroscopeCompassTilt Sensor
Sensors (v.1c) 5
Accelerometer
Functions: measure acceleration in one or more directions,
position can be deduced by integration. Orientation sensing : tilt sensor Vibration sensing
Methods: Mass spring method ADXL78 (from Analog Device )
Air pocket method (MX2125)
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ADXL78 (from Analog Device http://www.analog.com/UploadedFiles/Data_Sheets/ADXL78.pdf )Mass spring type (output acceleration in G)Measure the capacitance to create output
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ADXL330 accelerometer for three (X,Y,Z ) directions http://www.analog.com/UploadedFiles/Data_Sheets/ADXL330.pdf
3D
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2D translational accelerometerMX2125
Gas pocket typeWhen the sensor
moves, the temperatures of the 4 sensors are used to evaluate the 2D accelerations
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Accelerometer demo:orientation sensing
Self-balance RobotSensor demo
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Accelerometer demo :Tilt sensing demo
Tilt sensing demo
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Gyroscopes
Gyroscope Measure rotational angle
Rate Gyroscope measure the rate of rotation along 3-axes of X
(pitch), Y (roll), and Z (yaw). Modern implementations are using
Microelectromechanical systems (MEMS) technologies.
Gyroscope
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FEATURES Complete rate gyroscope on a single chip Microelectromechanical systems (MEMS) Z-axis (yaw-rate) response
APPLICATIONS GPS navigation systems Image stabilization Inertial measurement units Platform stabilization
Gyroscope to measure Rational acceleration ADXRS401
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Compass-- the Philips KMZ51 magnetic field sensor
50/60Hz (high) operation, a jitter of around 1.5°
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Rate gyroscope demo
Using Gyroscope compass for virtual reality application in an iphone
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Application of motion sensorsSelf balancing robot
by Kelvin Ko http://hk.youtube.com/watch?v=2u-EO2FDFG0
20cm
20cm
35cm35cm
Motion sensors: gyroscope and accelerometer
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Complementary filterComplementary filter
Since Since
Combine two sensors to find outputCombine two sensors to find output
1616
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Complementary filterComplementary filterθθ=rotation angle, =rotation angle, =filter time constant, s=laplace =filter time constant, s=laplace operator operator http://en.wikipedia.org/wiki/Low-pass_filter
1717
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Self Balanced robot using Self Balanced robot using complementary filtercomplementary filter
1818
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Tilt Sensor by OMRON
Detect tilting 35 ~ 65 degrees in right-and-left inclination
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Force/pressure/strain
Force-sensitive resistor (FSR)Strain gaugeFlexionAir pressure
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Force Sensing Resistors
FSR402
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Force Sensing Resistor Demo
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Application for a walking robot
Walking robot
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Application of force sensing resistance sensors to balance a walking robot
Balancing Floor tilled rightupper leg bend left
Floor tilled leftupper leg bend rightNeutral position
Four sensors under the foot
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Four Force sensors under the foot
D
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The Nao robot uses force feedback at its feet
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Strain Gauge : Force sensors
Piezoelectric crystal: produces a voltage that is proportional to force applied
Strain gauge: cemented on a rod. One end of the rod is fixed, force is applied to the other end. The resistance of the gauge will change with the force.
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Single element strain gauge
sensitive to temperature change.
resistance gauge unstrainedR
gauge theof length Lfactor, gauge strainG and G for
4424220
L
L
R
R
L
LGVb
R
RVb
RR
RV
RR
R
R
RVV bb
Vb
R
R R
Gauge=R+Rgauge
load
rodV0
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Four-element (Wheatstone bridge) strain gauge sensor,
Four times more sensitive than single gauge system; not sensitive to temperature change.
All gauges have unstrained resistance R.
L
LGV
R
RV
RRRR
RR
RRRR
RRVV bbb 2
20
b1=R-Rt2=R+ R
b2=R-R t1=R+RVb
t1 t2
b1 b2
rod
load
V0
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Flexion (bend) sensors
resistance: 10 KΩ (0°); 30-40 KΩ (90°) /
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Felixon resistance Demo
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Air pressure sensor
Measure up to 150 psi (pressure per square inch ).
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Position sensors
Infra-red range sensorLinear and Rotary position sensors
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Infra-red Range detectors by SHARP (4 to 30cm)
An emitter sends out light pulses. A small linear CCD array receives reflected light.
The distance corresponds to the triangle formed.
Sensors (v.1c) 35
IR radar using the Sharp range detector
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Position sensors, from[1]
Rotary Linear
Optical shaft encoder
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Magnetic rotary encoder)
non touch sensing
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Optical rotary encoder)
The light received (on or off) will tell the rotation angle)
3 light emitters
3 light receivers
Rotation shaft
Light paths
http://www.youtube.com/watch?v=RuIislTGOwA
Crank shaft sensor
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Temperature and humidity
Temperaturehumidity
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Temperature sensorsLM135/235/335 features(from NS)
Directly calibrated in °Kelvin 1°C initial accuracy available Operates from 400 µA to 5 mA Less than 1 Ohm dynamic impedance Easily calibrated Wide operating temperature range 200°C over range Low cost
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Application note (connecting to an ADC e.g. ADC0820 or ADC0801)
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Capacitive Atmospheric Humidity Sensor
BCcomponents 2322 691 90001 10-90%RH Dc
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Leaf Sensor Alerts When Plants Are Thirsty
Sensors (v.1c) 44
TSL250, TSL251, TSL252LIGHT-TO-VOLTAGE OPTICAL SENSORS
Light-to-voltage optical sensors, each combining a photodiode and an amplifier (feedback resistor = 16 MW, 8 MW, and 2 MW respectively).
The output voltage is directly proportional to the light intensity on the photodiode.
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Cadmium Sulfoselenide (CdS) Photoconductive Photocells
Light sensing using CdS
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Hall effect Sensors for sensing magnetic flux“B field”, see:
Sensors (v.1c) 47
Application on Magnetic levitation 磁懸浮
Magnetic levitation Train Model 磁懸浮火車
frog levitation
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Hall effect sensors and brushless DC motors
Brushless DC motor
Is it using Hall effect sensor? Don't known.
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Novel sensors
Kinect /
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Many KINECT DIY projects
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Control systemsExample: A temperature control
system
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Control example: Temperature control system
Temp.Sensor A/D
CPU
D/APulse Width modulation
& solid state relay
Heater
Timer
Sample&
Hold
Digital controlcircuit
Instrum. amp.
Water tank
computer
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Temperature control method 1: ON-Off (bang-bang) control (poor)
Easy to implement, bad control result -- contains overshoot undershot. Algorithm for on-off-control:
Loop forever: If (Tfrom_sensor > Treq required temperature)
then (heater off ) else (heater on).
Treq
Undershoot
Overshoot
Time
TempOn-off control result
Steady state error
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Temperature control method 2 : Proportional-integral-differential (PID) temperature control (good)
Init. (set required temperature Treq)
Loop forever{ get temperature T from sensor, e=T - Treq
then Tw =e*G*{Kp+Kd*[d(e)/dt] +Ki*e dt } else
} //G,Kp,Kd,Ki can be adjusted by user
Tw
Tw
Proportional, differential, integral
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PID block diagram
Figure 1 - Parallel PID block diagram
Kd
Ki
Kp
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PID control using pulse width modulation PWM
Fixed period and fixed number of pulses
Tw (depends on e )
Treq
PID control resultof method 2
On-off control: oscillates and unstable
Time
Temperature
Time
Sensors (v.1c) 57
Summary
Studied the characteristics of various sensors
and their applications